Troubleshooting PostgreSQL queries not using indexes

When PostgreSQL queries are not utilizing indexes effectively, it can significantly impact query performance. Here are some troubleshooting steps to identify and resolve issues with queries not using indexes efficiently:

  1. Check query execution plans: PostgreSQL provides the EXPLAIN command, which shows the execution plan for a query. Analyze the execution plan to see if it indicates any sequential scans (Seq Scan) instead of index scans (Index Scan or Bitmap Index Scan). Look for situations where the planner is choosing a suboptimal plan due to missing or ineffective indexes.
  2. Review query predicates: Examine the query predicates (conditions in the WHERE clause) to ensure they align with the indexed columns. If the query conditions do not match the indexed columns, PostgreSQL may resort to sequential scans. Adjusting the query conditions or adding appropriate indexes can improve index utilization.
  3. Analyze table statistics: Ensure that the table statistics are up to date. PostgreSQL relies on statistics to estimate the cost of various query plans. Outdated statistics can lead to suboptimal plan choices. Use the ANALYZE command to update table statistics or enable the autovacuum process to automatically collect statistics.
  4. Index maintenance: Ensure that the necessary indexes are present on the tables. Examine the query predicates and join conditions to identify columns that could benefit from indexing. Create or modify indexes based on the query patterns to improve index utilization.
  5. Consider index types: PostgreSQL offers different types of indexes, such as B-tree, hash, and GIN/GiST indexes. Evaluate the query requirements and data characteristics to determine the appropriate index type. Different index types excel in different scenarios, and choosing the right index type can improve query performance.
  6. Rewrite or optimize queries: Sometimes, queries may need to be rewritten or optimized to encourage index usage. Consider restructuring the query, introducing query hints (such as JOIN hints or INDEX hints), or using advanced features like partial indexes or expression indexes to better align the query with available indexes.
  7. Monitor and analyze query performance: Continuously monitor query performance using tools like pg_stat_statements and query logs. Identify frequently executed queries that suffer from poor index utilization and investigate possible solutions, such as index modifications, query rewriting, or schema redesign.
  8. Seek expert assistance: If the above steps do not yield satisfactory results or if you have complex performance issues, consider engaging a PostgreSQL performance tuning expert or consultant from MinervaDB who can analyze your specific workload, schema, and queries to provide targeted recommendations.

Remember that improving index utilization requires careful analysis of query patterns, table structures, and indexes. It’s important to test and validate any changes in a non-production environment before applying them to a production system.

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About Shiv Iyer 330 Articles
Open Source Database Systems Engineer with a deep understanding of Optimizer Internals, Performance Engineering, Scalability and Data SRE. Shiv currently is the Founder, Investor, Board Member and CEO of multiple Database Systems Infrastructure Operations companies in the Transaction Processing Computing and ColumnStores ecosystem. He is also a frequent speaker in open source software conferences globally.